In older Ubuntu releases one could change the sub-pixel rendering in the system settings, but that option was unfortunately removed in newer releases. Fortunately it is still accessible via gnome settings :
- In the left pane, go to /org/gnome/settings-daemon/plugins/xsettings
- In the right pane, change the value of the rgba-order key to bgr:
or via command line
gsettings set org.gnome.settings-daemon.plugins.xsettings rgba-order 'bgr'
 How can I change font rendering to sub-pixel BGR ordering?